The on/off button was never at the bottom on the iPhone. It's always been at the top or on the right side. Are you perhaps thinking of the home button (the round button below the screen on older models)? I have an iPhone X and I got used to not having a home button after about two days. You just swipe up from the bottom instead. When I help my wife with her phone I find that button annoying. I like having the whole front of the phone taken up by the screen because you get a bigger display without having to get a bigger phone. The iPhone X is about as big a phone as I'd want because anything larger feels too big for one-handed operation and doesn't fit well in my pockets.
